Preparation of nanoparticle materials

ABSTRACT

A method of producing nanoparticles comprises effecting conversion of a nanoparticle precursor composition to the material of the nanoparticles. The precursor composition comprises a first precursor species containing a first ion to be incorporated into the growing nanoparticles and a separate second precursor species containing a second ion to be incorporated into the growing nanoparticles. The conversion is effected in the presence of a molecular cluster compound under conditions permitting seeding and growth of the nanoparticles.

This application is the U.S. national stage application of International(PCT) Patent Application Serial No. PCT/GB2005/001611, filed Apr. 27,2005, which claims the benefit of GB Application No. 0409877.8, filedApr. 30, 2004. The entire disclosures of these two applications arehereby incorporated by reference as if set forth at length herein intheir entirety.

There has been substantial interest in the preparation andcharacterisation, because of their optical, electronic and chemicalproperties, of compound semiconductors consisting of particles withdimensions in the order of 2-100 nm,¹⁻⁸ Often referred to as quantumdots and/or nanocrystals. These studies have occurred mainly due totheir size-tuneable electronic, optical and chemical properties and theneed for the further miniaturization of both optical and electronicdevices^(9,10) that now range from commercial applications as diverse asbiological labelling, solar cells, catalysis, biological imaging,light-emitting diodes amongst many new and emerging applications.

Although some earlier examples appear in the literature,¹¹ recentlymethods have been developed from reproducible “bottom up” techniques,whereby particles are prepared atom-by-atom, i.e. from molecules toclusters to particles using “wet” chemical procedures.^(12,13) Ratherfrom “top down” techniques involving the milling of solids to finer andfiner powders.

To-date the most studied and prepared of semiconductor materials havebeen the chalcogenides II-VI materials namely ZnS, ZnSe, CdS, CdSe,CdTe; most noticeably CdSe due to its tuneability over the visibleregion of the spectrum. As mentioned semiconductor nanoparticles are ofacademic and commercial interest due to their differing and uniqueproperties from those of the same material, but in the macro crystallinebulk form. Two fundamental factors, both related to the size of theindividual nanoparticle, are responsible for their unique properties.The first is the large surface to volume ratio; as a particle becomessmaller, the ratio of the number of surface atoms to those in theinterior increases. This leads to the surface properties playing animportant role in the overall properties of the material. The secondfactor is that, with semiconductor nanoparticles, there is a change inthe electronic properties of the material with size, moreover, the bandgap gradually becoming larger because of quantum confinement effects asthe size of the particles decreases. This effect is a consequence of theconfinement of an ‘electron in a box’ giving rise to discrete energylevels similar to those observed in atoms and molecules, rather than acontinuous band as in the corresponding bulk semiconductor material.Thus, for a semiconductor nanoparticle, because of the physicalparameters, the “electron and hole”, produced by the absorption ofelectromagnetic radiation, a photon, with energy greater then the firstexcitonic transition, are closer together than in the correspondingmacrocrystalline material, so that the Coulombic interaction cannot beneglected. This leads to a narrow bandwidth emission, which is dependentupon the particle size and composition. Thus, quantum dots have higherkinetic energy than the corresponding macrocrystalline material andconsequently the first excitonic transition (band gap) increases inenergy with decreasing particle diameter.

Single core nanoparticles, which consist of a single semiconductormaterial along with an outer organic passivating layer, tend to haverelatively low quantum efficiencies due to electron-hole recombinationoccurring at defects and daggling bonds situated on the nanoparticlesurface which lead to non-radiative electron-hole recombinations. Onemethod to eliminate defects and daggling bonds is to grow a secondmaterial, having a wider band-gap and small lattice mismatch with thecore material, epitaxially on the surface of the core particle, (e.g.another II-VI material) to produce a “core-shell particle”. Core-shellparticles separate any carriers confined in the core from surface statesthat would otherwise act as non-radiative recombination centres. Oneexample is ZnS grown on the surface of CdSe cores. The shell isgenerally a material with a wider bandgap then the core material andwith little lattice mismatch to that of the core material, so that theinterface between the two materials has as little lattice strain aspossible. Excessive strain can further result in defects andnon-radiative electron-hole recombination resulting in low quantumefficiencies.

However, the growth of more than a few monolayers of shell material canhave the reverse effect thus; the lattice mismatch between CdSe and ZnS,is large enough that in a core-shell structure only a few monolayers ofZnS can be grown before a reduction of the quantum yield is observed,indicative of the formation of defects due to breakdown in the latticeas a result of high latticed strain. Another approach is to prepare acore-multi shell structure where the “electron-hole” pair are completelyconfined to a single shell such as the quantum dot-quantum wellstructure. Here, the core is of a wide bandgap material, followed by athin shell of narrower bandgap material, and capped with a further widebandgap layer, such as CdS/HgS/CdS grown using a substitution of Hg forCd on the surface of the core nanocrystal to deposit just 1 monolayer ofHgS.¹⁴ The resulting structures exhibited clear confinement ofphotoexcited carriers in the HgS layer.

The coordination about the final inorganic surface atoms in any core,core-shell or core-multi shell nanoparticles is incomplete, with highlyreactive “daggling bonds” on the surface, which can lead to particleagglomeration. This problem is overcome by passivating (capping) the“bare” surface atoms with protecting organic groups. The capping orpassivating of particles not only prevents particle agglomeration fromoccurring, it also protects the particle from its surrounding chemicalenvironment, along with providing electronic stabilization (passivation)to the particles in the case of core material. The capping agent usuallytakes the form of a Lewis base compound covalently bound to surfacemetal atoms of the outer most inorganic layer of the particle, but morerecently, so as to incorporate the particle into a composite, an organicsystem or biological system can take the form of, an organic polymerforming a sheaf around the particle with chemical functional groups forfurther chemical synthesis, or an organic group bonded directly to thesurface of the particle with chemical functional groups for furtherchemical synthesis.

Many synthetic methods for the preparation of semiconductornanoparticles have been reported, early routes applied conventionalcolloidal aqueous chemistry, with more recent methods involving thekinetically controlled precipitation of nanocrystallites, usingorganometallic compounds.

Over the past six years the important issues have concerned thesynthesis of high quality semiconductor nanoparticles in terms ofuniform shape, size distribution and quantum efficiencies. This has leadto a number of methods that can routinely produce semiconductornanoparticles, with monodispersity of <5% with quantum yields >50%. Mostof these methods are based on the original “nucleation and growth”method described by Murray, Norris and Bawendi,¹⁵ but use otherprecursors that the organometallic ones used. Murray et al originallyused organometallic solutions of metal-alkyls (R₂M) M=Cd, Zn, Te; R=Me,Et and tri-n-octylphosphine sulfide/selenide (TOPS/Se) dissolved intri-n-octylphosphine (TOP). These precursor solutions are injected intohot tri-n-octylphosphine oxide (TOPO) in the temperature range 120-400°C. depending on the material being produced. This produces TOPOcoated/capped semiconductor nanoparticles of II-VI material. The size ofthe particles is controlled by the temperature, concentration ofprecursor used and length of time at which the synthesis is undertaken,with larger particles being obtained at higher temperatures, higherprecursor concentrations and prolonged reaction times. Thisorganometallic route has advantages over other synthetic methods,including near monodispersity <5% and high particle crystallinity. Asmentioned, many variations of this method have now appeared in theliterature which routinely give high quality core and core-shellnanoparticles with monodispesity of <5% and quantum yield >50% (forcore-shell particles of as-prepared solutions), with many methodsdisplaying a high degree of size¹⁶ and shape¹⁷ control.

Recently attention has focused on the use of “greener”^(†) precursorswhich are less exotic and less expensive but not necessary moreenvironmentally friendly. Some of these new precursors include theoxides, CdO;¹⁸ carbonates MCO₃M=Cd, Zn; acetates M(CH₃CO₂)₂M=Cd, Zn andacetylacetanates [CH₃COCH═C(O⁻)CH₃]₂M=Cd, Zn; amongst other.^(19,20)^(†)(The use of the term “greener” precursors in semiconductor particlesynthesis has generally taken on the meaning of cheaper, readilyavailable and easier to handle precursor starting materials, than theoriginally used organometallics which are volatile and air and moisturesensitive, and does not necessary mean that “greener precursors” are anymore environmentally friendly).

Single-source precursors have also proved useful in the synthesis ofsemiconductor nanoparticle materials of II-VI, as well as other compoundsemiconductor nanoparticles.Bis(dialkyldithio-/diseleno-carbamato)cadmium(II)/zinc(II) compounds,M(E₂CNR₂)₂ (M=Zn or Cd, E=S or Se and R=alkyl), have used a similar‘one-pot’ synthetic procedure, which involved dissolving the precursorin tri-n-octylphosphine (TOP) followed by rapid injection into hottri-n-octylphosphine oxide/tri-n-octylphosphine (TOPO/TOP) above 200° C.

For all the above methods rapid particle nucleation followed by slowparticle growth is essential for a narrow particle size distribution.All these synthetic methods are based on the original organometallic“nucleation and growth” method by Murray et al¹⁵ which involves therapid injection of the precursors into a hot solution of a Lewis basecoordinating solvent (capping agent) which may also contain one of theprecursors. The addition of the cooler solution subsequently lowers thereaction temperature and assist particle growth but inhibits furthernucleation. The temperature is then maintained for a period of time,with the size of the resulting particles depending on reaction time,temperature and ratio of capping agent to precursor used. The resultingsolution is cooled followed by the addition of an excess of a polarsolvent (methanol or ethanol or sometimes acetone) to produce aprecipitate of the particles that can be isolated by filtration orcentrifugation.

Due to their increased covalent nature III-V and IV-VI highlycrystalline semiconductor nanoparticles are more difficult to prepareand much longer annealing time are usually required. However, there arenow many reports¹⁵ II-VI and IV-VI materials being prepared by a similarprocedure GaN,²¹ GaP,²² GaAs,^(22, 23, 24, 25, 26), InP^(27, 28, 29)InAs^(30, 27) and for PbS³¹ and PbSe.³²

Fundamentally all these preparations rely on the principle of particlenucleation followed by growth, moreover, to have a monodispersedensemble of nanoparticles there must be proper separation ofnanoparticles nucleation from nanoparticle growth. This is achieved byrapid injection of one or both precursors into a hot coordinatingsolvent (containing the other precursor if otherwise not present) whichinitiates particles nucleation, however, the sudden addition of thecooler solution upon injection subsequently lowers the reactiontemperature (the volume of solution added is about ⅓ of the totalsolution) and inhibits further nucleation maintaining a narrownanoparticle size distribution. Particle growth being a surfacecatalyzes process or via Ostwald ripening, depending on the precursor'sused³³, continues at the lower temperature and thus nucleation andgrowth are separated. This method works well for small scale synthesiswhere one solution can be added rapidly to another while keeping anhomogenous temperature throughout the reaction. However, on largerpreparative scale whereby large volumes of solution are required to berapidly injected into one another a temperature differential can occurwithin the reaction which can subsequently lead to a large particle sizedistribution.

Preparation from single-source molecular clusters, Cooney and co-workersused the cluster [S₄Cd₁₀(SPh)₁₆][Me₃NH]₄ to produce nanoparticles of CdSvia the oxidation of surface-capping SPh⁻ ligands by iodine. This routefollowed the fragmentation of the majority of clusters into ions whichwere consumed by the remaining [S₄Cd₁₀(SPh)₁₆]⁴⁻ clusters whichsubsequently grow into nanoparticles of CdS.³⁴ Strouse³⁵ and co-workersused a similar synthetic approach but employed thermolysis (lyothermal)rather than a chemical agent to initiate particle growth. Moreover, thesingle-source precursors [M₁₀Se₄(SPh)₁₆][X]₄ X=Li⁺ or (CH₃)₃NH⁺, M=Cd orZn were thermolysised whereby fragmentation of some clusters occursfollowed by growth of other from scavenging of the free M and Se ions orsimply from clusters aggregating to form larger clusters and then smallnanoparticles which subsequently continue to grow into larger particles.

According to the present invention there is provided a method ofproducing nanoparticles comprising effecting conversion of ananoparticle precursor composition to the material of the nanoparticles,said precursor composition comprising a first precursor speciescontaining a first ion to be incorporated into the growing nanoparticlesand a separate second precursor species containing a second ion to beincorporated into the growing nanoparticles, wherein said conversion iseffected in the presence of a molecular cluster compound underconditions permitting seeding and growth of the nanoparticles.

The present invention relates to a method of producing nanoparticles ofany desirable form and allows ready production of a monodispersepopulation of such particles which are consequently of a high purity. Itis envisaged that the invention is suitable for producing nanoparticlesof any particular size, shape or chemical composition. A nanoparticlemay have a size falling within the range 2-100 nm. A sub-class ofnanoparticles of particular interest is that relating to compoundsemiconductor particles, also known as quantum dots or nanocrystals.

An important feature of the invention is that conversion of theprecursor composition (comprising separate first and second precursorspecies) to the nanoparticles is effected in the presence of a molecularcluster compound (which will be other than the first or second precursorspecies). Without wishing to be bound by any particular theory, onepossible mechanism by which nanoparticle growth may take place is thateach identical molecule of the cluster compound acts as a seed ornucleation point upon which nanoparticle growth can be initiated. Inthis way, nanoparticle nucleation is not necessary to initiatenanoparticle growth because suitable nucleation sites are alreadyprovided in the system by the molecular clusters. The molecules of thecluster compound act as a template to direct nanoparticle growth.‘Molecular cluster’ is a term which is widely understood in the relevanttechnical field but for the sake of clarity should be understood hereinto relate to clusters of 3 or more metal or nonmetal atoms and theirassociated ligands of sufficiently well defined chemical structure suchthat all molecules of the cluster compound possess the same relativemolecular mass. Thus the molecular clusters are identical to one anotherin the same way that one H₂O molecule is identical to another H₂Omolecule. The use of the molecular cluster compound provides apopulation of nanoparticles that is essentially monodisperse. Byproviding nucleation sites which are so much more well defined than thenucleation sites employed in previous work the nanoparticles formedusing the method of the present invention possess a significantly morewell defined final structure than those obtained using previous methods.A further significant advantage of the method of the present inventionis that it can be more easily scaled-up for use in industry than currentmethods. Methods of producing suitable molecular cluster compounds areknown within the art, examples of which can be found at the CambridgeCrystallographic Data Centre (www.ccdc.ca.ac.uk).

The conversion of the precursor composition to nanoparticle is carriedout under conditions to ensure that there is either direct reaction andgrowth between the precursor composition and cluster, or some clustersgrow at the expense of others, due to Ostwald ripening, until reaching acertain size at which there is direct growth between the nanoparticleand the precursor composition. Such conditions ensure that themonodispersity of the cluster compound is maintained throughoutnanoparticle growth which, in turn, ensures that a monodispersepopulation of nanoparticles is obtained.

Any suitable molar ratio of the molecular cluster compound to first andsecond nanoparticle precursors may be used depending upon the structure,size and composition of the nanoparticles being formed, as well as thenature and concentration of the other reagents, such as the nanoparticleprecursor(s), capping agent, size-directing compound and solvent. It hasbeen found that particularly useful ratios of the number of moles ofcluster compound compared to the total number of moles of the first andsecond precursor species preferably lie in the range 0.0001-0.1 (no.moles of cluster compound):1 (total no. moles of first and secondprecursor species), more preferably 0.001-0.1:1, yet more preferably0.001-0.060:1. Further preferred ratios of the number of moles ofcluster compound compared to the total number of moles of the first andsecond precursor species lie in the range 0.002-0.030:1, and morepreferably 0.003-0.020:1. In particular, it is preferred that the ratioof the number of moles of cluster compound compared to the total numberof moles of the first and second precursor species lies in the range0.0035-0.0045:1.

It is envisaged that any suitable molar ratio of the first precursorspecies compared to the second precursor species may be used. Forexample, the molar ratio of the first precursor species compared to thesecond precursor species may lie in the range 100-1 (first precursorspecies):1 (second precursor species), more preferably 50-1:1. Furtherpreferred ranges of the molar ratio of the first precursor speciescompared to the second precursor species lie in the range 40-5:1, morepreferably 30-10:1. In certain applications it is preferred thatapproximately equal molar amounts of the first and second precursorspecies are used in the method of the invention. The molar ratio of thefirst precursor species compared to the second precursor speciespreferably lies in the range 0.1-1.2:1, more preferably, 0.9-1.1:1, andmost preferably 1:1. In other applications, it may be appropriate to useapproximately twice the number of moles of one precursor speciescompared to the other precursor species. Thus the molar ratio of thefirst precursor species compared to the second precursor species may liein the range 0.4-0.6:1, more preferably the molar ratio of the firstprecursor species compared to the second precursor species is 0.5:1. Itis to be understood that the above precursor molar ratios may bereversed such that they relate to the molar ratio of the secondprecursor species compared to the first precursor species. Accordingly,the molar ratio of the second precursor species compared to the firstprecursor species may lie in the range 100-1 (second precursorspecies):1 (first precursor species), more preferably 50-1:1, 40-5:1, or30-10:1. Furthermore, the molar ratio of the second precursor speciescompared to the first precursor species may lie in the range 0.1-1.2:1,0.9-1.1:1, 0.4-0.6:1, or may be 0.5:1.

The method of the present intention concerns the conversion of ananoparticle precursor composition to a desired nanoparticle. Suitableprecursor compositions comprise two or more separate precursor specieseach of which contains at least one ion to be included in the growingnanoparticle. The total amount of precursor composition required to formthe final desired yield of nanoparticles can be added beforenanoparticle growth has begun, or alternatively, the precursorcomposition can be added in stages throughout the reaction.

The conversion of the precursor composition to the material of thenanoparticles can be conducted in any suitable solvent. In the method ofthe present invention it is important to ensure that when the clustercompound and precursor composition are introduced in to the solvent thetemperature of the solvent is sufficiently high to ensure satisfactorydissolution and mixing of the cluster compound and precursorcomposition. Once the cluster compound and precursor composition aresufficiently well dissolved in the solvent the temperature of thesolution thus formed is raised to a temperature, or range oftemperatures, which is/are sufficiently high to initiate nanoparticlegrowth. The temperature of the solution can then be maintained at thistemperature or within this temperature range for as long as required toform nanoparticles possessing the desired properties.

A wide range of appropriate solvents are available. The particularsolvent used is usually at least partly dependent upon the nature of thereacting species, i.e. precursor composition and/or cluster compound,and/or the type of nanoparticles which are to be formed. Typicalsolvents include Lewis base type coordinating solvents, such as aphosphine (e.g. TOP), a phosphine oxide (e.g. TOPO) or an amine (e.g.HDA), or non-coordinating organic solvents, e.g. alkanes and alkenes. Ifa non-coordinating solvent is used then it will usually be used in thepresence of a further coordinating agent to act as a capping agent forthe following reason.

If the nanoparticles being formed are intended to function as quantumdots it is important to ensure that any dangling bonds on the surface ofthe nanoparticles are capped to minimise non-radiative electron-holerecombinations and inhibit particle agglomeration which can lowerquantum efficiencies. A number of different coordinating solvents areknown which can also act as capping or passivating agents, e.g. TOP,TOPO or HDA. If a solvent is chosen which cannot act as a capping agentthen any desirable capping agent can be added to the reaction mixtureduring nanoparticle growth. Such capping agents are typically Lewisbases but a wide range of other agents are available, such as oleic acidand organic polymers which form protective sheaths around thenanoparticles.

A further way to avoid problems related to non-radiative electron-holerecombinations is to grow one or more shells around the nanoparticlecore to form a ‘core-shell’ nanoparticle. Such shells are well known inthe art and are typically comprised of a different material to that ofthe core. The shell material is usually selected so as to have a widerband gap than the core material but to have as little lattice mismatchwith the core as possible to minimise lattice strain at the core-shellinterface which could lower quantum efficiencies due to non-radiativeelectron-hole recombinations.

The progress of nanoparticle growth can be monitored in any convenientway, such as photoluminescence (PL) or UV-visible (UV-vis) spectroscopy.Once nanoparticles have been produced having the desired properties,e.g. when a nanoparticle peak is observed on the PL/UV-vis emissionspectra at the desired wavelength, further growth is inhibited byaltering the reaction conditions, e.g. reducing the temperature of thesolution below that necessary to support nanoparticle growth. At thisstage the nanoparticles can be isolated immediately from solution by anyconvenient means, such as precipitation, or allowed to anneal at asuitable temperature for any desirable amount of time, e.g. 10 minutesto 72 hours, to ‘size-focus’ via Ostwald ripening prior to isolation.Following initial isolation, the nanoparticle material may then besubject to one or more rounds of washing to provide a final product ofhigh purity.

It is also envisaged that a shape directing compound, such as aphosphonic acid derivative, may be added to the reaction mixture toencourage the growing nanoparticles to adopt a particular shape, e.g.spheres, rods, disks, tetrapods or stars, which may be of use inparticular applications.

The invention comprises of a method to produce nanoparticle materialsmainly but not restricted to compound semiconductor nanoparticles fromthe use of molecular clusters, whereby the clusters are definedidentical molecular entities, as compared to ensembles of smallnanoparticles, which inherently lack the anonymous nature of molecularclusters. The invention consists of the use of molecular clusters astemplates to seed the growth of nanoparticles, whereby other molecularsources “molecular feedstocks” are used to facilitate particle growth.These molecular feedstocks are a combination of separate precursors eachcontaining one or more element/ion required within the as to be grownnanoparticles.

Type of System to be Made

The present invention is directed to the preparation of a number ofnanoparticles materials and includes compound semiconductor particlesotherwise referred to as quantum dots or nanocrystals, within the sizerange 2-100 nm and include core material comprising of:—

IIA-VIB (2-16) material, consisting of a first element from group 2 ofthe periodic table and a second element from group 16 of the periodictable and also including ternary and quaternary materials and dopedmaterials. Nanoparticle material include but are not restricted to:—MgS,MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe.

IIB-VIB (12-16) material consisting of a first element from group 12 ofthe periodic table and a second element from group 16 of the periodictable and also including ternary and quaternary materials and dopedmaterials. Nanoparticle material includes but are not restrictedto:—ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe.

II-V material consisting of a first element from group 12 of theperiodic table and a second element from group 15 of the periodic tableand also including ternary and quaternary materials and doped materials.Nanoparticle material include but is not restricted to:—Zn₃P₂, Zn₃As₂,Cd₃P₂, Cd₃As₂, Cd₃N₂, Zn₃N₂.

III-V material consisting of a first element from group 13 of theperiodic table and a second element from group 15 of the periodic tableand also including ternary and quaternary materials and doped materials.Nanoparticle material include but is not restricted to:—BP, AlP, AlAs,AlSb; GaN, GaP, GaAs, GaSb; InN, InP, InAs, InSb, AlN, BN.

III-IV material consisting of a first element from group 13 of theperiodic table and a second element from group 16 of the periodic tableand also including ternary and quaternary materials and doped materials.Nanoparticle material include but is not restricted to:—B₄C, A₄C₃, Ga₄C.

III-VI material consisting of a first element from group 13 of theperiodic table and a second element from group 16 of the periodic tableand also including ternary and quaternary materials. Nanoparticlematerial include but is not restricted to:—Al₂S₃, Al₂Se₃, Al₂Te₃, Ga₂S₃,Ga₂Se₃, GeTe; In₂S₃, In₂Se₃, Ga₂Te₃, In₂Te₃, InTe.

IV-VI material consisting of a first element from group 14 of theperiodic table and a second element from group 16 of the periodic table,and also including ternary and quaternary materials and doped materials.Nanoparticle material include but is not restricted to:—PbS, PbSe, PbTe,Sb₂Te₃, SnS, SnSe, SnTe.

Nanoparticle material consisting of a first element from any group inthe transition metal of the periodic table, and a second element fromany group of the d-block elements of the periodic table and alsoincluding ternary and quaternary materials and doped materials.Nanoparticle material include but is not restricted to:—NiS, CrS,CuInS₂.

By the term doped nanoparticle for the purposes of specifications andclaims, refer to nanoparticles of the above and a dopant comprised ofone or more main group or rare earth elements, this most often is atransition metal or rare earth element, such as but not limited to zincsulfide with manganese, such as ZnS nanoparticles doped with Mn⁺.

Ternary Phase

By the term ternary phase nanoparticle for the purposes ofspecifications and claims, refer to nanoparticles of the above but athree component material. The three components are usually compositionsof elements from the as mentioned groups Example being(Zn_(x)Cd_(x-1)S)_(m)L_(n) nanocrystal (where L is a capping agent).

Quaternary Phase

By the term quaternary phase nanoparticle for the purposes ofspecifications and claims, refer to nanoparticles of the above but afour-component material. The four components are usually compositions ofelements from the as mentioned groups Example being(Zn_(x)Cd_(x-1)S_(y)Se_(y-1))_(m)L_(n) nanocrystal (where L is a cappingagent).

Solvothermal

By the term Solvothermal for the purposes of specifications and claims,refer to heating the reaction solution so as to initiate and sustainparticle growth and can also take the meaning solvothermal, thermolysis,thermolsolvol, solution-pyrolysis, lyothermal.

Core-Shell and Core/Multi Shell Particles

The material used on any shell or subsequent numbers of shells grownonto the core particle in most cases will be of a similar lattice typematerial to the core material i.e. have close lattice match to the corematerial so that it can be epitaxially grown on to the core, but is notnecessarily restricted to materials of this compatibility. The materialused on any shell or subsequent numbers of shells grown on to the corepresent in most cases will have a wider band-gap then the core materialbut is not necessarily restricted to materials of this compatibility.The materials of any shell or subsequent numbers of shells grown on tothe core can include material comprising of:—

IIA-VIB (2-16) material, consisting of a first element from group 2 ofthe periodic table and a second element from group 16 of the periodictable and also including ternary and quaternary materials and dopedmaterials. Nanoparticle material include but is not restricted to:—MgS,MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe.

IIB-VIB (12-16) material consisting of a first element from group 12 ofthe periodic table and a second element from group 16 of the periodictable and also including ternary and quaternary materials and dopedmaterials. Nanoparticle material include but is not restricted to:—ZnS,ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe.

II-V material consisting of a first element from group 12 of theperiodic table and a second element from group 15 of the periodic tableand also including ternary and quaternary materials and doped materials.Nanoparticle material include but is not restricted to:—Zn₃P₂, Zn₃As₂,Cd₃P₂, Cd₃As₂, Cd₃N₂, Zn₃N₂.

III-V material consisting of a first element from group 13 of theperiodic table and a second element from group 15 of the periodic tableand also including ternary and quaternary materials and doped materials.Nanoparticle material include but is not restricted to:—BP, AlP, AlAs,AlSb; GaN, GaP, GaAs, GaSb; InN, InP, InAs, InSb, AlN, BN.

III-IV material consisting of a first element from group 13 of theperiodic table and a second element from group 16 of the periodic tableand also including ternary and quaternary materials and doped materials.Nanoparticle material include but is not restricted to:—B₄C, Al₄C₃,Ga₄C.

III-VI material consisting of a first element from group 13 of theperiodic table and a second element from group 16 of the periodic tableand also including ternary and quaternary materials. Nanoparticlematerial include but is not restricted to:—Al₂S₃, Al₂Se₃, Al₂Te₃, Ga₂S₃,Ga₂Se₃, In₂S₃, In₂Se₃, Ga₂Te₃, In₂Te₃.

IV-VI material consisting of a first element from group 14 of theperiodic table and a second element from group 16 of the periodic tableand also including ternary and quaternary materials and doped materials.Nanoparticle material include but is not restricted to:—PbS, PbSe, PbTe,Sb₂Te₃, SnS, SnSe, SnTe.

Nanoparticle material consisting of a first element from any group inthe transition metal of the periodic table, and a second element fromany group of the d-block elements of the periodic table and alsoincluding ternary and quaternary materials and doped materials.Nanoparticle material include but is not restricted to:—NiS, CrS,CuInS₂.

Outer Most Particle Layer

Capping Agent

The outer most layer (capping agent) of organic material or sheathmaterial is to inhibit particles aggregation and to protect thenanoparticle from the surrounding chemical environment and to provide ameans of chemical linkage to other inorganic, organic or biologicalmaterial. The capping agent can be the solvent that the nanoparticlepreparation is undertaken in, and consists of a Lewis base compoundwhereby there is a lone pair of electrons that are capable of donor typecoordination to the surface of the nanoparticle and can include momo- ormulti-dentate ligands of the type but not restricted to:—phosphines(trioctylphosphine, triphenolphosphine, t-butylphosphine), phosphineoxides (trioctylphosphine oxide), alkyl-amine (hexadecylamine,octylamine), ary-amines, pyridines, and thiophenes.

The outer most layer (capping agent) can consist of a coordinated ligandthat processes a functional group that can be used as a chemical linkageto other inorganic, organic or biological material such as but notrestricted to:—mercaptofunctionalized amines or mercaptocarboxylicacids.

The outer most layer (capping agent) can consist of a coordinated ligandthat processes a functional group that is polymerisable and can be usedto form a polymer around the particle, polymerisable ligands such as butnot limited to styrene functionalized amine, phosphine or phosphineoxide ligand.

Nanoparticle Shape

The shape of the nanoparticle is not restricted to a sphere and canconsist of but not restricted to a rod, sphere, disk, tetrapod or star.The control of the shape of the nanoparticle is by the addition of acompound that will preferentially bind to a specific lattice plane ofthe growing particle and subsequently inhibit or slow particle growth ina specific direction. Example of compounds that can be added but is notrestricted to include:—phosphonic acids (n-tetradecylphosphonic acid,hexylphoshonic acid, 1-decanesulfonic acid, 12-hydroxydodecanoic acid,n-octadecylphosphonic acid).

Description of Preparative Procedure

The current invention should lead to pure, monodispersed,nanocrystalline particles that are stabilized from particle aggregationand the surrounding chemical environment by an organic layer, where Mand E are two different elements in a (ME)_(m)L_(y) particles and Lbeing the coordinating organic layer/capping agent, such as a II-VIsemiconductor (ZnS)_(n)(TOPO)_(y) nanoparticle constituting of a ZnScore surrounded by trioctylphosphine oxide ligands (TOPO).

The first step for preparing nanoparticles of a semiconductor materialis to use a molecular cluster as a template to seed the growth ofnanoparticles from other element source precursors. This is achieved bymixing small quantity of a cluster which is to be used as the templatewith a high boiling solvent which can also be the capping agent, being aLewis base coordination compound such as but not restricted to aphosphine, a phosphine oxide or an amine such as TOP, TOPO or HDA; or aninert solvent such as a alkane (octadecence) with the addition of acapping agent compound such as oleic acid. Further to this a source forM and a source for E (for a ME particle) are added to the reactionmixture. The M and E precursor are in the form of two separateprecursors one containing M and the other containing E.

Further to this other regents may or may not be added to the reactionswhich have the ability to control the shape of the nanoparticles grown.These additives are in the form of a compound that can preferentiallybind to a specific face (lattice plane) of the growing nanoparticle andthus inhibit or slow grow along that specific direction of the particle.Other element source precursors may or may not be added to the reactionso as to produce ternary, quaternary or doped particles.

Initially, the compounds of the reaction mixture are allowed to mix on amolecular level at a low enough temperature where no particle growthwill occur. The reaction mixture is then heated at a steady rate untilparticle growth is initiated upon the surfaces of the molecularcluster-templates. At an appropriate temperature after the initiation ofparticle growth further quantities of M and E precursors may be added tothe reaction mixture if needed so as to inhibit particles consuming oneanother by the process of Ostward ripening. Further precursor additioncan be in the form of batch addition whereby solid precursor orsolutions containing precursor are added over a period of time or bycontinuous dropwise addition. Because of the complete separation ofparticle nucleation and growth, the current invention displays a highdegree of control in terms of particle size, which is controlled by thetemperature of the reaction and concentrations of precursors present.Once the desired particle size is obtained, as established from UVand/or PL spectra of the reaction solution either by an in situ opticalprobe or from aliquots of the reaction solution, the temperature may ormay not be reduced by ca. 30-40° C. and the mixture left to “size-focus”for a period of time being from 10 minutes to 72 hours.

Further consecutive treatment of the as formed nanoparticles to formcore-shell or core-multi shell particles may be undertaken. Core-shellparticle preparation is undertaken either before or after nanoparticleisolation, whereby the nanoparticles are isolated from the reaction andredissolved in new (clean) capping agent as this results in a betterquantum yield. A source for N and a source for Y precursor are added tothe reaction mixture and can be either in the form of two separateprecursors one containing N and the other containing Y or as asingle-source precursor that contains both N and Y within a singlemolecule to form a core-shell particle of ME/NY core-shell material.

The process may be repeated with the appropriate element precursorsuntil the desired core-multi shell material is formed. The nanoparticlessize and size distribution in an ensemble of particles is dependent bythe growth time, temperature and concentrations of reactants insolution, with higher temperatures producing larger nanoparticles.

Type of Cluster used for Seeding

The invention includes the use of molecular clusters, whereby theclusters used are identical molecular entities as compared tonanoparticles, which inherently lack the anonymous nature of molecularclusters in an assembly. The clusters act as “embryo-type” templates forthe growth of nanoparticles whereby other molecular sources precursorscontribute ions to the growth process and thus clusters subsequentlygrow into particles. The molecular clusters to be used can consist of:—

Both elements required within the as to be grown nanoparticle eitherwith or without other elements present plus organic moieties;

One element required within the as to be grown nanoparticle either withor without other elements present plus organic moieties;

Neither element required within the as to be grown nanoparticle eitherwith or without other elements present plus organic moieties;

The requirement of a cluster used, is to initiate particle growth eithervia consumption of other clusters or from reaction with the precursorspresent. Thus, the cluster can be used as a template for particlegrowth.

Examples, clusters to be used but not restricted to include:—

IIB-VIB:—[{(PPh₃)Hg}₄(SPh)₆]: (Ph₄P)₂[(SEt)₅(Br)(HgBr)₄]:(Ph₄P)₂[Hg₄(SEt)₅Br]: [Hg₄Te₁₂][N(CH₂CH₂Et)₄]₄

IIB-VIB:—[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆]; [RME^(t)Bu]₅ M=Zn, Cd, Hg; E=S, Se,Te; R=Me, Et, Ph: [X]₄[E₄M₁₀(SR)₁₆] E=S, Se, Te, M=Zn, Cd, Hg; X=Me₃NH⁺,Li⁺, Et₃NH⁺: [Cd₃₂S₁₄(SPh)₃₆].L: [Hg₁₀Se₄(SePh)(PPh₂ ^(n)Pr)₄];[Hg₃₂Se₁₄(SePh)₃₆]; [Cd₁₀Se₄(SePh)₁₂(PPr₃)₄]; [Cd₃₂Se₁₄(SePh)₃₆(PPh₃)₄];[M₄(SPh)₁₂]⁺[α]₂ ⁻ M=Zn, Cd, Hg; X=Me₄N⁺, Li⁺: [Zn(SEt)Et]₁₀: [MeMEiPr]M=Zn, Cd, Hg; E=S, Se, Te: [RCdSR′]₅ R=O(ClO₃), R′=PPh₃, ^(i)Pr:[Cd₁₀E₄(E′Ph)₁₂(PR₃)₄] E, E′=Te, Se, S: [Cd₈Se(SePh)₁₂Cl₄]²⁻: [M₄Te₁₂]⁴⁻M=Cd, Hg: [Ph₁₂M₁₈Cd₁₀(PEt₃)₃] M=Te, Se:

II-V:—[RCdNR′]₄ R=Cl, Br, I, PEt₃, C=CSMe₃; R′=PEt₃, I: [RCdNR′]₅R=alkyl or aryl group and R′=alkyl or aryl group: [{RZn}₆{PR′}₄] R=I,PEt₂Ph, R′=SiMe₃: [M₄Cl₄(PPh₂)₄(P^(n)Pr₃)₂] M=Zn, Cd:[Li(thf)₄]₂[(Ph₂P)₁₀Cd₄]: [Zn₄(PPh₂)₄Cl₄(PRR₂′)₂] PRR′₂=PMe^(n)Pr₂,P^(n)Bu₃, PEt₂Ph: [Zn₄(P^(t)Bu₂)₄Cl₄]

III-V [EtGaNEt]₆; [MeGaN(4-C₆H₄F)]₆; (MeGaNiBu)₆; [RAlNR′]₄ R=Me,CH₂Pr^(i), Ph; R′=Pr^(i), CH₂Pr^(i), C₆H₂Me₃; [(SiPr^(i) ₃)₃AsAlH]₆;[^(i)PrNAlH]₄; [RAlNR′]₆ R=Me, Et, Cl, CH₂Ph, CH₂Pr^(i), Ph; R′=Me H,Br, C=CPh, Pr^(i), (CH₂)₂Me, (CH₂)2NMe₂, SiPh₃: [CH₃Ga—NCH₂CH(CH₃)₂]₆:[MeGaN^(i)Bu]₆: [RGaNR′]₄ R=Ph, Me; R′=Ph, C₆F₅, SiMe₃, ^(t)Bu:[EtGaNEt]₆: [RGaPR′]₄ R=^(i)Pr, C₆H₂Me₃; R′=^(t)Bu: C₆H₂Me₃: [RNInR′]₄R=Cl, Br, I, Me; R′=^(t)Bu, C₆F₅, C₆H₄F: [RInPR′]₄ R=^(i)Pr, C₆H₂Me₃,Et; R′=SiPh₃, C₆H₂Me₃, Si^(i)Pr₃: [RInPR′]₆ R=Et, R′=SiMe₂(CMe₂ ^(i)Pr)

III-VI [(^(t)Bu)GaSe]₄; [^(t)BuGaS]₇; [RInSe]₄ R=^(t)Bu, CMe₂Et,Si(^(t)Bu)₃, C((SiMe₃)₃)₃; [RInS]₄ R=^(t)Bu, CMe₂Et; [RGaS]₄ R=^(t)Bu,CMe₂Et, CEt₃: [SAlR′]₄ R=C(SMe₃)₃, CEtMe₂: [SAlNMe₃]₅: [TeAlR]4 R=Cp*,CEtMe₂: [(C(SiMe₃)₃)GaS]₄: [^(t)BuGaS]₆: [RGaSe]₄ R=^(t)Bu, CMe₂Et,CEt₃, C(SiMe₃)₃, Cp*, Bu: Cd₄In₁₆S₃₃.(H₂O)₂₀(C₁₀H₂₈N₄)_(2.5):

IV-VI [S₆{SnR}₄] R=C(SiMe₃)₃, Me, Ph; [Se₆{SnR}₄] R=C₆F₅, C₆H₂Me₃,p-Tol, C(SiMe₃)₃

Material consisting of a first element from any group in the transitionmetals of the periodic table and a second element from any group of thed-block elements include but are not restricted to:—[Cu₁₂Se₆(PR₃)₈]R=Et₂Ph, ^(n)Pr₃, Cy₃; [Cu₁₈Te₆(^(t)Bu)₆(PPh₂Et)₇];[Cu₁₉Te₆(^(t)Bu)₇(PEt₃)₈]; [Cu₂₇Te₁₅(P^(i)Pr₂Me)₁₂]; [Ni₃₄Se₂₂(PPh₃)₁₀];[Ag₃₀(TePh)₁₂Te₉(PEt₃)₁₂]; [Ag₃₀Se₈(Se^(t)Bu)₁₄(PnPr₃)₈];[Co4(μ₃-Se)₄(PPh₃)₄]; [CO₆(μ₃-Se)₈(PPh₃)₆]; [W₃Se₄(dmpe)₃Br₃]⁺;Ru₄Bi₂(CO)₁₂; Fe₄P₂(CO)₁₂; Fe₄N₂(CO)₁₂

M Source

For a compound semiconductor nanoparticle consisting of elements(ME)_(n)L_(m) a source for element M is further added to the reactionand can consist of any M-containing species that has the ability toprovide the growing particles with a source of M ions. The precursor canconsist of but are not restricted to an organometallic compound, aninorganic salt, a coordination compound or the element.

Examples for II-VI, III-V, III-VI or IV-V for the first element includebut are not restricted to:—

Organometallic such as but not restricted to a MR₂ where M=Mg R=alkyl oraryl group (Mg^(t)Bu₂); MR₂ where M=Zn, Cd, Te; R=alkyl or aryl group(Me₂Zn, Et₂Zn Me₂Cd, Et₂Cd); MR₃ Where M=Ga, In, Al, B; R=alkyl or arylgroup [AlR₃, GaR₃, InR₃ (R=Me, Et, ^(i)Pr)].

Coordination compound such as a carbonate but not restricted to a MCO₃M=Ca, Sr, Ba, [magnesium carbonate hydroxide [(MgCO₃)₄Mg(OH)₂]; M(CO₃)₂M=Zn, Cd; MCO₃ M=Pb: acetate: M(CH₃CO₂)₂ M=Mg, Ca, Sr, Ba; Zn, Cd, Hg;M(CH₃CO₂)₃ M=B, Al, Ga, In: a β-diketonate or derivative thereof, suchas acetylacetonate (2,4-pentanedionate) M[CH₃COCH═C(O⁻)CH₃]₂ M=Mg, Ca,Sr, Ba, Zn, Cd, Hg; M[CH₃COCH═C(O⁻)CH₃]₃ M=B, Al, Ga, In. OxalateSrC₂O₄, CaC₂O₄, BaC₂O₄, SnC₂O₄. Hydroxide M(OH)₂ M=Mg, Ca, Sr, Ba, Zn,Cd, Hg, e.g. Cd(OH)₂. Sterate M(C₁₇H₃₅COO)₂ M=Mg, Ca, Sr, Ba, Zn, Cd,Hg.

Inorganic salt such as but not restricted to a Oxides SrO, ZnO, CdO,In₂O₃, Ga₂O₃, SnO₂, PbO₂; Nitrates Mg(NO₃)₂, Ca(NO₃)₂, Sr(NO₃)₂,Ba(NO₃)₂, Cd(NO₃)₂, Zn(NO₃)₂, Hg(NO₃)₂, Al(NO₃)₃, In(NO₃)₃, Ga(NO₃)₃,Sn(NO₃)₄, Pb(NO₃)₂

An element Mg, Ca, Sr, Ba, Zn, Cd, Hg, B, Al, Ga, In, Sn, Pb.

E Source

For a compound semiconductor nanoparticle consisting of elements(ME)_(n)L_(m) a source for element E is further added to the reactionand can consist of any E-containing spices that has the ability toprovide the growing particles with a source of E ions. The precursor canconsist of but are not restricted to an organometallic compound, aninorganic salt, a coordination compound or an elemental source. Examplesfor an II-VI, III-V, III-VI or IV-V semiconductor were the secondelement include but are not restricted to:—

Organometallic such as but not restricted to a NR₃, PR₃, AsR₃, SbR₃(R=Me, Et, ^(t)Bu, ^(i)Bu, Pr^(i), Ph etc.); NHR₂, PHR₂, AsHR₂, SbHR₂(R=Me, Et, ^(t)Bu, ^(i)Bu, Pr^(i), Ph etc.); NH₂R, PH₂R, AsH₂R, SbH₂R₃(R=Me, Et, ^(t)Bu, ^(i)Bu, Pr^(i), Ph etc.); PH₃, AsH₃; M(NMe)₃ M=P, Sb,As; dimethyldrazine (Me₂NNH₂); ethylazide (Et-NNN); hydrazine (H₂NNH₂);Me₃SiN₃.

MR₂ (M=S, Se Te; R=Me, Et, ^(t)Bu, ^(i)Bu etc.); HMR (M=S, Se Te; R=Me,Et, ^(t)Bu, Bu, ^(i)Pr, Ph etc); thiourea S═C(NH₂)₂; Se═C(NH₂)₂.

Sn(CH₄)₄, Sn(C₄H₉), Sn(CH₃)₂(OOCH₃)₂.

Coordination compound such as but not restricted to a carbonate, MCO₃M=P, bismuth subcarbonate (BiO)₂CO₃; M(CO₃)₂; acetate M(CH₃CO₂)₂ M=S,Se, Te: M(CH₃CO₂)₂ M=Sn, Pb or M(CH₃CO₂)₄ M=Sn, Pb: a β-diketonate orderivative thereof, such as acetylacetonate (2,4-pentanedionate)[CH₃COCH═C(O⁻)CH₃]₃M M=Bi; [CH₃COCH═C(O⁻)CH₃]₂M M=S, Se, Te:[CH₃COCH═C(O⁻)CH₃]₂M M=Sn, Pb: thiourea, selenourea (H₂NC(═Se)NH₂.

Inorganic salt such as but not restricted to Oxides P₂O₃, As₂O₃, Sb₂O₃,Sb₂O₄, Sb₂O₅, Bi₂O₃, SO₂, SeO₂, TeO₂, Sn₂O, PbO, PbO₂; NitratesBi(NO₃)₃, Sn(NO₃)₄, Pb(NO₃)₂

An element:—Sn, Ge, N, P, As, Sb, Bi, S, Se, Te, Sn, Pb.

The present invention is illustrated with reference to the followingnon-limiting Examples and accompanying figures, in which:

FIG. 1) is a diagram of a) core particle consisting of a CdSe core andHDA as an organic capping agent, b) core-shell particle consisting of aCdSe core a ZnS shell and HDA as an organic capping agent, c) core-multishell organic capped particle consisting of a CdSe core a HgS shellfollowed by a ZnS shell with a HDA capping agent;

FIG. 2) Molecular clusters used as seeding agents: a) Zn₁₀(SEt)₁₀E₁₀; b)[RGaS]₄; c) [Bu^(t)GaS]₇; d) [RInSe]₄; and e) [X]₄[M₁₀Se₄(SPh)₁₆]X=cation, M=Zn, Cd, Te;

FIG. 3) Formation of a Cadmium selenide quantum dot using[M₁₀Se₄(SPh)₁₆][X]₄ X=Li⁺ or (CH₃)₃NH⁺, Et₃NH⁺ as the molecular seed andcadmium acetate and tri-n-octylphosphine selenide as the cadmium andselenium element-source precursors and with Hexadecylamine used as thecapping agent;

FIG. 4) Formation of a Gallium sulfide quantum dot using [^(t)BuGaS]₇ asthe molecular seed and gallium(II)acetylacetonate andtri-n-octylphosphine sulfide as the gallium and sulfide element-sourceprecursors and with Hexadecylamine used as the capping agent;

FIG. 5) Formation of a indium selenide quantum dot using as themolecular seed and Indium(II)acetylacetonate and tri-n-octylphosphinesulfide as the Indium and selenide element-source precursors and withHexadecylamine and tri-n-octylphosphine oxide used as the capping agent;

FIG. 6) Formation of a zinc sulfide quantum dot using Zn₁₀(SEt)₁₀Et₁₀ asthe molecular seed and zinc acetate and tri-n-octylphosphine sulfide asthe zinc and sulfur element-source precursors and with Hexadecylamineused as the capping agent;

FIG. 7) Evolution of the PL spectra of CdSe nanoparticles as thenanoparticles become bigger during growth. Preparation from[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆]/TOPSe/Cd(CH₃CO₂)₂ in HDA in accordance withExample 1;

FIG. 8) Evolution of the PL spectra of CdSe nanoparticles as thenanoparticles become bigger during growth. Preparation from[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆]/TOPSe/Cd(CH₃CO₂)₂ in HDA in accordance withExample 2;

FIG. 9) Evolution of the PL spectra of CdSe nanoparticles as thenanoparticles become bigger during growth. Preparation from[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆]/TOP/Se/CdO in HDA in accordance with Example 3;

FIG. 10) Evolution of the PL spectra of CdSe nanoparticles as thenanoparticles become bigger during growth. Preparation from[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆]/TOPSe/Cd(OH)₂ in HDA in accordance with Example4;

FIG. 11) Evolution of the PL spectra of CdSe nanoparticles as thenanoparticles become bigger during growth. Preparation from[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆]/TOPSe/Me₂Cd in HDA in accordance with Example5;

FIG. 12) Evolution of the PL spectra of CdSe nanoparticles as thenanoparticles become bigger during growth. Preparation from[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆]/TOPSe/(C₁₇H₃₅COO)₂Cd in HDA in accordance withExample 7;

FIG. 13) Evolution of the PL spectra of CdSe nanoparticles as thenanoparticles become bigger during growth. Preparation from[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆]/TOPSe/CdCO₃ in HDA in accordance with Example8;

FIG. 14) Evolution of the PL spectra of CdTe nanoparticles as thenanoparticles become bigger during growth. Preparation from[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆]/Te as a slurry in TOP/Cd(CH₃CO₂)₂ in HDA inaccordance with Example 9.

EXAMPLES

All syntheses and manipulations were carried out under a dry oxygen-freeargon or nitrogen atmosphere using standard Schlenk or glove boxtechniques. All solvents were distilled from appropriate drying agentsprior to use (Na/K-benzophenone for THF, Et₂O, toluene, hexanes andpentane). HDA, octylamine, TOP, Cd(CH₃CO₂)₂, selenium powder, CdO, CdCO₃(Adrich) were procured commercially and used without furtherpurification.

UV-vis absorption spectra were measured on a Heλiosβ Thermospectronic.Photoluminescence (PL) spectra were measured with a Fluorolog-3 (FL3-22)photospectrometer at the excitation wavelength 380 nm. Powder X-Raydiffraction (PXRD) measurements were preformed on a Bruker AXS D8diffractometer using monochromated Cu—K_(α) radiation.

For all methods all capping agent solutions were dried and degassedbefore use by heating the mixture to 120° C. under a dynamic vacuum forat lest 1 hour. The reaction mixture was then cooled to the desiredtemperature for that particular reaction before any seeding agent orgrowth precursors were added to the solution.

Cluster Preparation Preparation of [HNEt₃]₂[Cd₄(SPh)₁₀]

To a stirred methanol (60 ml) solution of benzenethiol (20.00 g, 182mmol) and triethylamine (18.50 g, 182 mmoL) was added dropwiseCd(NO₃)₂.4H₂O (21.00 g, 68.00 mmol) that had previously been dissolvedin methanol (60 mL). The solution was then allowed to stir while warminguntil the precipitate had completely dissolved to leave a clearsolution. This was then place at 5° C. for 24 h in which time largecolourless crystals of [HNEt₃]₂[Cd₄(SPh)₁₀] had formed. FW=1745.85.Anal. Calcu for C₇₂H₈₂N₂S₁₀Cd₄ C=49.53; H=4.70; N=1.61; S=18.37;Cd=25.75%. Found C=49.73; H=4.88; N=1.59; S=17.92%.

Preparation of [HNEt₃]₄[Cd₁₀Se₄(SPh)₁₆]

This was by a similar procedure to that described by Dance et al³⁶.

To a stirred acetonitrile (100 ml) solution of [HNEt₃]₂[Cd₄(SPh)₁₀](80.00 g, 45.58 mmol) was added 3.57 g 45.21 mmol of selenium powder,the resulting slurry was left to stir for 12 hours, this produced awhite precipitate. A further 750 ml of acetonitrile was added and thesolution warmed to 75° C. to give a clear pale yellow solution which wasallowed to cool to 5° C., yielding large colourless crystals. Thecrystals were washed in hexane and recrystallized from hot acetonitrile.To give 22.50 g of [HNEt₃]₄[Cd₁₀Se₄(SPh)₁₆]. FW=3595.19 Anal. Calc forC₁₂₀H₁₄₄N₄Se₄S₁₆Cd₁₀. C=40.08; H=4.00; N=1.56; S=14.27; Se=8.78;Cd=31.26%. Found C=40.04; H=4.03; N=1.48; S=14.22; Cd=31.20%.

Example 1 Preparation of CdSe Nanoparticles from[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆]/TOPSe/Cd(CH₃CO₂)₂ in HDA

HDA (300 g) was placed in a three-neck flask and dried/degassed byheating to 120° C. under a dynamic vacuum for 1 hour. The solution wasthen cooled to 70° C. To this was added 1.0 g of[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆] (0.311 mmol), TOPSe (20 ml, 40.00 mmol)[previously prepared from dissolving selenium powder in TOP] andCd(CH₃CO₂)₂ (10.66 g 40.00 mmol) the temperature of reaction mixture wasgradually increased from 70° C. to 180° C. over an 8 hour period. Theprogressive formation/growth of the nanoparticles was monitored by theiremission wavelength by taking aliquots from the reaction mixture andmeasuring their UV-vis and PL spectra. The reaction was stopped when theemission spectra had reached 572 nm by cooling the reaction to 60° C.followed by addition of 200 ml of dry “warm” ethanol which gave aprecipitation of nanoparticles. The resulting CdSe were dried beforere-dissolving in toluene filtering through Celite followed byre-precipitation from warm ethanol to remove any excess HDA andCd(CH₃CO₂)₂. This produced 9.26 g of HDA capped CdSe nanoparticles.

Example 2 Preparation of CdSe Nanoparticles from[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆]/TOPSe/Cd(CH₃CO₂)₂ in HDA

HDA (250 g) and octylamine (20 g) was placed in a three-neck flask anddried/degassed by heating to 120° C. under a dynamic vacuum for 1 hour.The solution was then cooled to 70° C. To this was added 1.0 g of[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆] (0.311 mmol), TOPSe (1M, 4 ml, 4.00 mmol)[previously prepared from dissolving selenium powder in TOP] andCd(CH₃CO₂)₂ dissolved in TOP (0.5M, 4 ml, 2.00 mmol) the temperature ofreaction mixture was gradually increased from 70° C. to 150° C. over ahour period. A further 17 ml (17.00 mmol) of TOPSe and 27 ml of a 0.5MCd(CH₃CO₂)₂ dissolved in TOP (13.50 mmol) were added dropwise while thetemperature was gradually increased to 200° C. over a 24 h period. Theprogressive formation/growth of the nanoparticles was monitored by theiremission wavelength by taking aliquots from the reaction mixture andmeasuring their UV-vis and PL spectra. The reaction was stopped when theemission spectra had reached the desired size 630 nm by cooling thereaction to 60° C. followed by addition of 200 ml of dry “warm” ethanolwhich gave a precipitation of particles. The resulting CdSe were driedbefore re-dissolving in toluene filtering through Celite followed byre-precipitation from warm ethanol to remove any excess HDA. Thisproduced 4.56 g of HDA capped CdSe nanoparticles.

Example 3 Preparation of CdSe Nanoparticles from[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆]/TOP/Se/CdO in HDA

HDA (150 g) and t-decylphosphonic acid (0.75 g) was placed in athree-neck flask and dried and degassed by heating to 120° C. under adynamic vacuum for 1 hour. The solution was then cooled to 80° C. Tothis was added 0.5 g of [Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆] (0.156 mmol), 20 ml ofTOP, 0.6 g of selenium powder (7.599 mmol) and 0.8 g CdO (6.231 mmol)the reaction mixture was allowed to stir to give a pale red cloudymixture. The temperature of the reaction mixture was gradually increasedfrom 80° C. to 250° C. over a period of 24 h. The progressiveformation/growth of the nanoparticles was followed by their emissionwavelength by taking aliquots from the reaction mixture and measuringtheir UV-vis and PL spectra. The reaction was stopped when the emissionspectra had reached the desired size (593 nm) by cooling the reaction to60° C. followed by addition of 200 ml of dry “warm” ethanol, which gavea precipitation of particles. The resulting CdSe were dried beforere-dissolving in toluene filtering through Celite followed byre-precipitation from warm ethanol to remove any excess HDA. Thisproduced 1.55 g of HDA capped CdSe nanoparticles.

Example 4 Preparation of CdSe Nanoparticles from[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆]/TOPSe/Cd(HO)₂ in HDA

HDA (400 g) was placed in a three-neck flask and dried and degassed byheating to 120° C. under a dynamic vacuum for 1 hour. The solution wasthen cooled to 70° C. To this was added 1.00 g of[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆] (0.278 mmol), 20.0 ml of TOPSe, (2M solution)and 5.85 g of Cd(OH)₂ (40.00 mmol), the reaction mixture was allowed tostir to give a pale yellow cloudy mixture. The temperature of thereaction mixture was gradually increased from 70° C. to 240° C. over aperiod of 24 h. The progressive formation/growth of the nanoparticleswas followed by their emission wavelength by taking aliquots from thereaction mixture and measuring their UV-vis and PL spectra. The reactionwas stopped when the emission spectra had reached the desired size (609nm) by cooling the reaction to 60° C. followed by addition of 200 ml ofdry “warm” ethanol, which gave a precipitation of particles. Theresulting CdSe were dried before re-dissolving in toluene filteringthrough Celite followed by re-precipitation from warm ethanol to removeany excess HDA. This produced 10.18 g of HDA capped CdSe nanoparticles.

Example 5 Preparation of CdSe Nanoparticles from[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆]/TOPSe/Me₂Cd in HDA

HDA (10 g) was placed in a three-neck flask and dried and degassed byheating to 120° C. under a dynamic vacuum for 1 hour. The solution wasthen cooled to 70° C. To this was added 0.13 g of[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆] (0.036 mmol), 2.5 ml of TOPSe, (2M solution)and 0.71 g Me₂Cd [that had previously been dissolved in TOP] (0.358 ml,5.00 mmol) the reaction mixture was allowed to stir. The temperature ofthe reaction mixture was gradually increased from 80° C. to 260° C. overa period of 24 h. The progressive formation/growth of the nanoparticleswas followed by their emission wavelength by taking aliquots from thereaction mixture and measuring their UV-Vis and PL spectra. The reactionwas stopped when the emission spectra had reached the desired size (587nm) by cooling the reaction to 60° C. followed by addition of 100 ml ofdry “warm” ethanol, which gave a precipitation of particles. Theresulting CdSe were dried before re-dissolving in toluene filteringthrough Celite followed by re-precipitation from warm ethanol to removeany excess HDA. This produced 1.52 g of HDA capped CdSe nanoparticles.

Example 6 Preparation of CdSe Nanoparticles from[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆]/TOPSe/Me₂Cd in HDA

HDA (100 g) was placed in a three-neck flask and dried and degassed byheating to 120° C. under a dynamic vacuum for 1 hour. The solution wasthen cooled to 70° C. To this was added 0.13 g of[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆] (0.036 mmol). The temperature was thenincreased to 100° C. and maintained at this temperature while 2.5 ml ofTOPSe, (2M solution) and 0.71 g Me₂Cd [that had previously beendissolved in TOP] (0.358 ml, 5.00 mmol) were added dropwise over a 4hour period. The progressive formation/growth of the nanoparticles wasfollowed by their emission wavelength by taking aliquots from thereaction mixture and measuring their UV-Vis and PL spectra. The reactionwas stopped when the emission spectra had reached the desired size (500nm) by cooling the reaction to 60° C. followed by addition of 100 ml ofdry “warm” ethanol, which gave a precipitation of particles. Theresulting CdSe were dried before re-dissolving in toluene filteringthrough Celite followed by re-precipitation from warm ethanol to removeany excess HDA. This produced 1.26 g of HDA capped CdSe nanoparticles.

Example 7 Preparation of CdSe Nanoparticles from[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆]/TOPSe/(C₁₇H₃₅COO)₂Cd in HDA

HDA (200 g) was placed in a three-neck flask and dried and degassed byheating to 120° C. under a dynamic vacuum for hour. The solution wasthen cooled to 80° C. To this was added 0.5 g of[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆] (0.139 mmol), 20 ml of TOPSe (2M solution) anda solution of 2.568 g CdO (20 mmol) previously dissolved in steric acid(23.00 g), the reaction mixture was allowed to stir to give a paleyellow clear solution. The temperature of the reaction mixture wasgradually increased from 70° C. to 220° C. over a period of 24 h. Theprogressive formation/growth of the nanoparticles was followed by theiremission wavelength by taking aliquots from the reaction mixture andmeasuring their UV-vis and PL spectra. The reaction was stopped when theemission spectra had reached the desired size (590 nm) by cooling thereaction to 60° C. followed by addition of 400 ml of dry “warm” ethanol,which gave a precipitation of particles. The resulting CdSe were driedbefore re-dissolving in toluene filtering through Celite followed byre-precipitation from warm ethanol to remove any excess HDA. Thisproduced 4.27 g of HDA capped CdSe nanoparticles.

Example 8 Preparation of CdSe Nanoparticles from[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆]/TOPSe/CdCO₃ in HDA

HDA (50 g) was placed in a three-neck flask and dried/degassed byheating to 120° C. under a dynamic vacuum for 1 hour. The solution wasthen cooled to 75° C. To this was added 0.5 g of[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆] (0.156 mmol), TOPSe (1.0M, 5 ml, 5.00 mmol)[previously prepared from dissolving selenium powder in TOP] and CdCO₃dissolved in TOP (0.5M, 5 ml, 2.50 mmol) the temperature of reactionmixture was gradually increased from 70° C. to 200° C. over a 48 hperiod. The progressive formation/growth of the nanoparticles weremonitored by their emission wavelength by taking aliquots from thereaction mixture and measuring their UV-vis and PL spectra. The reactionwas stopped when the emission spectra had reached the desired size (587nm) by cooling the reaction to 60° C. followed by addition of 200 ml ofdry “warm” ethanol which gave a precipitation of particles. Theresulting CdSe were dried before re-dissolving in toluene filteringthrough Celite followed by re-precipitation from warm ethanol to removeany excess HDA. This produced 0.95 g of HDA capped CdSe nanoparticles.

Example 9 Preparation of CdTe Nanoparticles from[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆]/TOPTe/Cd(CH₃CO₂)₂ in RDA

HDA (200 g) was placed in a three-neck flask and dried/degassed byheating to 120° C. under a dynamic vacuum for 1 hour. The solution wasthen cooled to 70° C. To this was added 1.0 g of[Et₃NH]₄[Cd₁₀Se₄(SPh)₁₆] (0.31 mmol), a brown slurry of TOP (20 ml) withtellurium (2.55 g, 20.00 mmol) along with Cd(CH₃CO₂)₂ (4.33 g, 20.00mmol) was added. The temperature of reaction mixture was graduallyincreased from 70° C. to 160° C. over an 8 hour period. The progressiveformation/growth on the CdTe nanoparticles was monitored by theiremission wavelengths by taking aliquots from the reaction mixture andmeasuring their UV-vis and PL spectra. The reaction was stopped when theemission spectra had reached (624 nm) by cooling the reaction to 60° C.followed by addition of 200 ml of dry “warm” ethanol which gave aprecipitation of particles. The resulting CdTe were dried beforerecrystallizing from toluene followed by re-precipitation from warmethanol to remove any excess HDA. This produced 6.92 g of HDA cappedCdTe nanoparticles.

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1. A method of producing nanoparticles comprising: effecting conversionof a nanoparticle precursor composition to a material of thenanoparticles, said precursor composition comprising a first precursorspecies containing a first ion to be incorporated into the nanoparticlesand a separate second precursor species containing a second ion to beincorporated into the nanoparticles, wherein said conversion is effectedin the presence of a molecular cluster compound different from the firstprecursor species and the second precursor species under conditionspermitting seeding and growth of the nanoparticles.
 2. A method inaccordance with claim 1, wherein a ratio of a number of moles of thecluster compound to a total number of moles of the first and secondprecursor species is selected from a range of 0.0001-0.1:1.
 3. A methodin accordance with claim 1, wherein a molar ratio of the first precursorspecies to the second precursor species is selected from a range of100-1:1.
 4. A method in accordance with claim 1, wherein the molecularcluster compound and nanoparticle precursor composition are dissolved ina solvent at a first temperature to form a solution and a temperature ofthe solution is then increased to a second temperature sufficient toinitiate seeding and growth of the nanoparticles on the molecularclusters of said compound.
 5. A method in accordance with claim 4,wherein the first temperature is selected from a range of 50° C. to 100°C.
 6. A method in accordance with claim 4, wherein the secondtemperature is selected from a range of 120° C. to 280° C.
 7. A methodin accordance with claim 1, wherein effecting conversion of thenanoparticle precursor composition comprises: a) monitoring an averagesize of the nanoparticles being grown; and b) terminating nanoparticlegrowth when the average nanoparticle size reaches a predetermined value.8. A method in accordance with claim 7, wherein nanoparticle growth isterminated by reducing the temperature of the solution from the secondtemperature to a third temperature.
 9. A method in accordance with claim8, wherein the third temperature is selected from a range of 50° C. to70° C.
 10. A method in accordance with claim 1, wherein the methodcomprises forming a precipitate of the nanoparticle material by additionof a precipitating reagent.
 11. A method in accordance with claim 1,wherein the first precursor species is selected from the groupconsisting of an organometallic compound, an inorganic salt, and acoordination compound.
 12. A method in accordance with claim 1, whereinthe first precursor species is obtained by dissolving in a suitablesolvent an elemental source selected from the group consisting of Mg,Ca, Sr, Ba, Zn, Cd, Hg, B, Al, Ga, In, Sn, and Pb.
 13. A method inaccordance with claim 1, wherein the second precursor species isselected from the group consisting of an organometallic compound, aninorganic salt, and a coordination compound.
 14. A method in accordancewith claim 1, wherein the second precursor species is obtained bydissolving in a suitable solvent an elemental source selected from thegroup consisting of Sn, Ge, N, P, As, Sb, Bi, S, Se, Te, Sn and Pb. 15.A method in accordance with claim 1, wherein the molecular clustercompound comprises a third ion and a fourth ion to be incorporated intothe nanoparticles.
 16. A method in accordance with claim 15, wherein thethird ion is selected from group 12, 13, 14, or 15 or from thetransition metal group of the periodic table and further wherein: (i) ifthe third ion is selected from group 12 or 13 of the periodic table,then the fourth ion is selected from group 15 or 16 of the periodictable; and (ii) if the third ion is selected from group 14 of theperiodic table, then the fourth ion is selected from group 16 of theperiodic table; and (iii) if the third ion is selected from thetransition metal group of the periodic table, then the fourth ion isselected from the d-block of the periodic table.
 17. A method inaccordance with claim 1, wherein the nanoparticles have cores comprisinga core compound comprising fifth and sixth ions.
 18. A method inaccordance with claim 17, wherein each nanoparticle comprises at leastone shell grown onto the nanoparticle core.
 19. A method in accordancewith claim 18, wherein the at least one shell has a lattice type similarto a lattice type of the nanoparticle core.
 20. A method in accordancewith claim 18, wherein the at least one shell has a wider band-gap thana band-gap of the nanoparticle core.
 21. A method in accordance withclaim 1, wherein the nanoparticles are ternary phase nanoparticles orquaternary phase nanoparticles.
 22. A method in accordance with claim 1,wherein the nanoparticles comprise outer most layers comprising acapping agent.
 23. A method in accordance with claim 22, wherein thecapping agent is a solvent in which the nanoparticles are grown.
 24. Amethod in accordance with claim 22, wherein the capping agent is a Lewisbase.
 25. A method of producing nanoparticles comprising effectingconversion of a nanoparticle precursor composition to a material of thenanoparticles, said precursor composition comprising a first precursorspecies containing a first ion to be incorporated into the nanoparticlesand a separate second precursor species containing a second ion to beincorporated into the nanoparticles, said conversion being effected inthe presence of a molecular cluster compound different from the firstprecursor species and the second precursor species under conditionspermitting seeding and growth of the nanoparticles, wherein themolecular cluster compound and nanoparticle precursor composition aredissolved in a solvent at a first temperature to form a solution and thetemperature of the solution is then increased to a second temperaturewhich is sufficient to initiate seeding and growth of the nanoparticleson the molecular clusters of said compound.